1. Field of the Invention
The present invention relates to an array substrate, a method of manufacturing the array substrate and a liquid crystal display (LCD) apparatus having the array substrate. More particularly, the present invention relates to an array substrate capable of decreasing light leakage and afterimage and capable of increasing transmittance and reflectance, a method of manufacturing such array substrate, and an LCD apparatus having the array substrate.
2. Discussion of the Related Art
LCD apparatuses are well-known display devices. In LCD devices, images are displayed by controlling the transmission of light through a layer of liquid crystals. The liquid crystals change their orientation in response to electric field, and the orientation of the liquid crystals determines how much light passes through the liquid crystal layer. Thus, by controlling the voltage that is applied to electrodes surrounding the liquid crystal layer in a plurality of pixels, the desired image can be displayed.
The liquid crystals do not generate light on their own—they block or transmit light from a separate source. Thus, a typical LCD apparatus incorporates an internal light source, a reflective surface that allows utilization of light coming from a source external to the apparatus, or both. A transmissive-type LCD apparatus, which displays images by using an internal light source, requires a battery for power supply. This requirement for a battery is disadvantageous, as the battery increases the weight and the size of the LCD apparatus. A reflective-type LCD apparatus, which relies on an external source for light supply, does not need a battery. However, the reflective LCD apparatus suffers from another disadvantage of the device luminance depending on the amount of ambient light that is available. In a dark environment, for example, the reflective-type LCD apparatus will not demonstrate high luminance.
Reflective-transmissive-type LCD apparatuses that include both an internal light source and a reflective surface do not suffer either of the disadvantages described above to the extent that the reflective-type or the transmissive-type LCD apparatuses do. A reflective-transmissive-type LCD apparatus displays images by transmitting the light from the internal light source and reflecting any external light. The internal light source allows the apparatus to maintain a desired level of luminance regardless of the amount of ambient light that is available. At the same time, since the apparatus is able to utilize external light when external light is available, power is conserved and a large battery is not necessary.
FIGS. 1 and 2 show a conventional reflective-transmissive LCD apparatus 10. Although a backlight assembly that provides the internal light is part of the apparatus, it is not shown in the Figures. FIG. 1 is a plan view and FIG. 2 is a cross-sectional view taken along the line A-A′ of FIG. 1. As shown in FIG. 1 and FIG. 2, the conventional LCD apparatus 10 has a contact hole.
The LCD apparatus 10 includes a first member 170, a second member 180, and a liquid crystal layer 108. The first member 170 includes a first substrate 100, a black matrix 102, a color filter 104, a first electrode 106, and a spacer 110. The second member 180 includes a second substrate 120, a thin film transistor 119, a gate insulating layer 126, a passivation layer 116, an organic layer 114, a second electrode 112 and a reflective electrode 113. Part of the organic layer 114 is removed to form an opening 129, which defines a transmissive region 150. The area outside the opening 129 that includes a thick layer of the organic layer 114 forms a reflective region 160. A contact hole 128 extends through the organic layer 114. The second member 180 has a pixel region 140 and a peripheral region 145. The transmissive region 150 and the reflective region 160 are located in the pixel region 140.
The liquid crystals in the LCD apparatus may be arranged in the mixed twisted nematic (MTN) mode or the homogeneous mode. In the MTN mode, the liquid crystals are twisted at an angle that is no greater than 90°. When the liquid crystals are arranged in the MTN mode, light is polarized to decrease light transmittance. When the liquid crystals are arranged in the homogeneous mode, the transmittance of the reflective-transmissive LCD apparatus increases. In a reflective-transmissive-type LCD apparatus with liquid crystals in the homogeneous mode, the light from the internal light source enters the liquid crystal layer from a second member 180, passes through the liquid crystals, and exits the LCD apparatus by passing through a first member 170. The externally provided light, on the other hand, reaches the liquid crystal layer through the first member 170 and is reflected back out of the apparatus by the reflective electrode 113.
The thin film transistor 119, which is disposed in the reflective region 160, includes a source electrode 118a, a gate electrode 118b, a drain electrode 118c, and a semiconductor layer pattern. The source electrode 118a is electrically connected to a source line 118a′ and the gate electrode 118b is electrically connected to a gate line 118b′. The drain electrode 118c is electrically connected to the second electrode 112 and the reflective electrode 113 through the contact hole 128. To electrically couple the reflective electrode to the TFT, the contact hole is located in the reflective region 160 and extends through the organic layer that separates the reflective electrode from the TFT.
The reflective region 160 and the transmissive region 150 have different cell gaps. A “cell gap” is the space between the first member 170 and the second member 180 that is occupied by the liquid crystals. Typically, the cell gap in the transmissive region 150 is larger than the cell gap in the reflective region 160 (e.g., the cell gap in the transmissive region is about twice as large as the cell gap in the reflective region). The cell gaps are determined by the thickness of an organic layer formed on the second substrate 120 in the reflective and transmissive regions.
Since the organic layer does not uniformly coat the second substrate, “steps” form where the thickness of the organic layer transitions. For example, steps form at the interface between the transmissive region 150 and the reflective region 160, and at the contact hole 128. The presence of these steps is disadvantageous because the orientation of liquid crystals is difficult to control near these steps. As a result of these steps that are formed, light leakage and afterimage occur. Light leakage occurs mostly in an area of the transmissive region 150 around where rubbing is started, and afterimage occurs near where the rubbing ends. Light leakage occurs independently of the applied voltage while the severity of afterimage depends on the applied voltage. Both light leakage and afterimage deteriorate the display quality of an LCD apparatus.
The contact hole 128 is undesirable not just because it creates a step region but also because it adversely affects the reflectance of the LCD apparatus. Light reflectance in the contact hole 128 is not as high as reflectance in the other parts of the reflective region because of the larger cell gap in the contact hole 128. Thus, it is desirable to eliminate the contact hole 128.
A method of manufacturing an LCD with reduced light leakage and afterimage is desirable.